Re: [PATCH v2 00/17] net: introduce Qualcomm IPA driver

On Wed, 2019-06-26 at 15:58 +0200, Arnd Bergmann wrote:

quoted

The IPA hardware is actually something that sits *between* the
AP and the modem.  It implements one form of communication
pathway (IP data), but there are others (including QMI, which
presents a network-like interface but it's actually implemented
via clever use of shared memory and interrupts).

Can you clarify how QMI fits in here? Do you mean one has to
talk to both IPA and QMI to use the modem, or are these two
alternative implementations for the same basic purpose?

I'm not going to comment on QMI specifically, because my understanding
might well be wrong, and any response to your question will likely
correct my understanding :-)

(Thus, you should probably also ignore everything I ever said about QMI)

My previous understanding was that from the hardware perspective
there is only one control interface, which is for IPA. Part of this
is abstracted to user space with ioctl commands to the IPA driver,
and then one must set up rmnet to match these by configuring
an rmnet device over netlink messages from user space, but
rmnet does not have a control protocol with the hardware.

Right so this is why I say it's confusing when we just talk about
"control interface" or "path".

I see multiple layers of control

 * hardware control, which you mention here. This might be things like
   "enable/disable aggregation on an rmnet channel" etc. I guess this
   type of thing would have been implemented with ioctls? Not the
   aggregation specifically, but things that affect how you set up the
   hardware.

 * modem control, which we conflate, but can be like AT commands or
   MBIM. From the kernel driver POV, this is actually just another
   channel it provides for userspace to talk to the modem.

johannes